Engine mount - build or buy?

Hey folks,

I'm getting to the pointy end of the 701 build and starting to pore over the plans for the 912/912s engine mount.

The one in the plans is the bed-style mount as shown below:

I seem to remember that to buy a firewall-forward kit was somewhere north of $4,000.  Not including engine, obviously.  Zenair site quotes the bed mount by itself as US $750, so with freight and currency conversion that could be over $1500.  

Before I start planning in SketchUp, building a jig and contacting my long-suffering metal worker to tell him there's more 4130 welding on the way... is there a better option?  Are these mounts "standard" or easily modified from other aircraft (and is it common that they're sold second hand?) 

What are the advantages of the newer "ring" style mount over the "bed" style?

If building, are there traps to look out for?  Is it a different level of welding?  

All helpful comments appreciated.  Thanks!

Marty

I'm told ring mounts are better. I know one aircraft with a ring mount and the lack of vibration and smoothness are obvious.

I don't know whether it just his setup/engine but he recons it's the mount. I can tell it's him taxiing past my hanger over any other rotax.

Just so quiet and smooth.

Could you purchase the cut tube, and then weld here? Might save on postage.

You know the schrader valve and gauge trick?

I have a bed mount but also an arm over the top from firewall to gbox....

You know the schrader valve and gauge trick?

Er... no?  Please explain!

Could you purchase the cut tube, and then weld here? Might save on postage.

Think I've actually got enough 4130 to do the job.  So yes I could cut it and prep for welding.

Weld up your mount fully sealed. Fit a schrader valve and small pressure gauge.

Put a little bit of air pressure in your mount. (A few psi)

If your mount cracks you will lose air pressure.

Weld up your mount fully sealed. Fit a schrader valve and small pressure gauge.Put a little bit of air pressure in your mount. (A few psi)

 

If your mount cracks you will lose air pressure.

Thanks for that.  According to the bed mount plans the front tubes are open (guess I could always weld caps on the ends).

have recently finished installing the older bottom style engine mount to my 701 and found it easier than the newer ring mount to fit. Asa for the smoother rotax motor, I would put that down to the newer cdi system which allows for smoother start ups and engine idling, it can be fitted to earlier models. The older style mount provide for better fixing of radiators etc. and when removing motor for servicing can be handled by two people actually man handling the motor, stripped of course. I have however fixed backing plates to fire wall connections with m6 bolts which are bigger than zenith recommends I believe. Have also sealed fire wall with fire proof sealant which gives added benefit of less noise entering the cockpit area. Hope this advice helps.

Hi Marty I have bed mount for a Savannha hanging in the shed if you want to copy it .I have finally got my 701  in the air it has a 582  they are a lot of fun to fly 

cheers phil

Hi Marty I have bed mount for a Savannha hanging in the shed if you want to copy it .I have finally got my 701  in the air it has a 582  they are a lot of fun to fly cheers phil

Hi Phil,

Whereabouts are you?  I'd love to take a look if you're in southern Tas.

Cheers, Marty

I dunno, I would tend to get people experienced in the actual area to do the job, it's a critical safety part in my mind.

Could try Ole http://www.aircraftkits.com.au/    They have plenty of experience mounting Rotax to STOL.

Hi Marty 

I,m in Portland vic if you are over this way, happy to take you for a fly.I have been watching your build I don't think you would have to much trouble building one .If you pay some body to build you one you won't get much change out of $2500.

Cheers Phil

Hi Marty I,m in Portland vic if you are over this way, happy to take you for a fly.I have been watching your build I don't think you would have to much trouble building one .If you pay some body to build you one you won't get much change out of $2500.

 

Cheers Phil

Thanks Phil.  Had to look up where Portland is... I would've been through there on the motorbike about 20 years ago on the way to Adelaide, haven't been since!

I might see what kind of welding job this bloke does on my cabin frame first, if it's excellent work I reckon I'd trust him with the engine mount.

I dunno, I would tend to get people experienced in the actual area to do the job, it's a critical safety part in my mind.Could try Ole http://www.aircraftkits.com.au/    They have plenty of experience mounting Rotax to STOL.

Good idea Bex - will contact him.